gs -q -dNOPAUSE -sDEVICE=tiffg4 -sOutputFile=files/tx.tiff files/T38_TEST_PAGES.pdf -c quit
gs -q -dNOPAUSE -sDEVICE=tiffg4 -sOutputFile=files/tx.tiff files/invoice.pdf -c quit
docker exec freeswitch1 /usr/local/freeswitch/bin/fs_cli -x "originate {absolute_codec_string='PCMU'}sofia/external/[email protected]:5062 &txfax(/files/tx.tiff)"
scp HCT_SERVER:/opt/fax/files/rx.tiff ./files/
tiff2pdf -o T38_TEST_PAGES_faxed.pdf -p A4 -F rx.tiff
https://developer.signalwire.com/freeswitch/FreeSWITCH-Explained/Modules/mod_spandsp_6587021/#fax